Here in the original manuscript, Oliver Cowdery initially omitted the now but then virtually immediately inserted it supralinearly (there is no difference in the level of ink flow). Since either reading is theoretically possible, the critical text will follow the corrected reading in 𝓞, a decision supported by the fact that in Alma’s discourses to his three sons, he uses “and now my son” 22 times but never “and my son”.
Summary: Maintain in Alma 42:29 the corrected reading in 𝓞, “and now my son”; such usage is prominent in Alma’s discourses to his sons.